1. Field of the Invention
The field of art to which this invention pertains is oil recovery methods using surfactants and mobility control of surfactant slugs in oil recovery processing. Relevant art is contained in U.S. Classification 166-273, 274, and 275.
2. Detailed Description of the Prior Art
Relevant prior art includes additive compositions including those characterized as water-insoluble mineral oil additives which are produced from the reaction of alkenyl-substituted succinic acid anhydrides and a tertiary amine as disclosed in U.S. Pat. No. 2,588,412. Oil-soluble polyvalent metal salts of an alkenyl-succinic acid monoamide are also disclosed in U.S. Pat. No. 2,458,425. Both of these patents are classified in U.S. Classification 260-561 and are limited to the use of such materials as additives for mineral oil or lube oil uses.
It has been recognized in the petroleum industry that oil recovery methods using surfactants can be used to effectively remove oil from a subterranean reservoir which has been subjected to straight water flooding or polymer flooding operations. Without the use of surfactants or materials which can help remove this oil from the interstitial spaces within the reservoir, it is essentially non-recoverable.
The art has also recognized that when using surfactants many problems exist when these materials are used in reservoirs of elevated temperatures (temperatures around 140.degree. F. or higher). An especially acute problem which results when passing surfactants into high-temperature reservoirs is that they will lose viscosity and will not perform to their optimum capabilities. Accordingly, then, mobility control additives are useful when added to such surfactant materials. Such thickening agents include materials such as heteropolysaccharides produced by the bacteria of the genus Xanthomonas. More particularly, such materials are disclosed in U.S. Pat. No. 3,964,972.
The use of thickeners in surfactant slugs is disclosed, at least concerning using the polysaccharide materials, in U.S. Pat. No. 3,719,606 in which microemulsions of oil-soluble alkali metal sulfonates are used along with co-surfactants and from about 0.05 to about 1 percent by weight of a polysaccharide to enhance the viscosity of the microemulsion for improved oil recovery.
Some of the thickening agents now present on the market, including materials such as hydrolyzed polyacrylamides or copolymers of sodium acrylates or methacrylates and acrylamide, generally are not good candidates for use in surfactant slugs for oil recovery since in many instances these materials are not compatible with materials such as crude oil sulfonates, gas oil sulfonates or aliphatic polymer sulfonates. Many of the polyacrylamide-type materials when mixed with sulfonate surfactants precipitate forming coagulated gels which may increase the residual resistance of an oil-containing reservoir to a point that moving additional fluid through it becomes very difficult if not impossible.
Many of the thickeners used, such as the polysaccharides or other water-soluble polymers, themselves do not contain sufficient surfactant properties to be used in a surfactant slug without reducing the surfactant's ability to move oil unless additional surfactant is used.
It would therefore be advantageous to use water-soluble thickeners which also possess surfactant properties in order that an increase in the viscosity of a surfactant fluid could be attained without losing surfactant properties by dilution of the surfactant by the water-soluble polymer. Accordingly, the present invention attains this ideal situation by including, in one instance, in a surface-acting fluid a viscosity-enhancing additive material which also contains sufficient surfactant moieties in order to act both as a viscosity thickening agent and a surfactant agent.
In another instance, the present invention provides a surfactant which possesses sufficient viscosifying properties in order that it may be used by itself in certain instances for recovery of oil from oil reservoirs where high viscosity surfactants are necessarily needed.